In recent years as an environmentally friendly vehicle hybrid vehicles have been developed into practical use. A hybrid vehicle has mounted therein an internal combustion engine as a normal vehicular power source, and in addition thereto an electric motor generating force to drive the vehicle, and a power supply system for supplying electric power to drive the motor. The power supply system includes a power storage device.
For hybrid vehicles, there has been proposed a configuration charging a vehicle-mounted power storage device by a power supply external to the vehicle (hereinafter also referred to as an “external power supply”), and accordingly, there is a demand for increased distances travelable on electric power stored in the vehicle-mounted power storage device. Hereinafter, charging a vehicle-mounted power storage device by an external power supply will also simply be referred to as “external charging”.
For example, Japanese Patent Laying-Open No. 2008-109840 (PTL 1) describes a power supply system having a plurality of power storage devices (batteries) connected in parallel. The power supply system described in PTL 1 is provided with a voltage converter (a converter) for each power storage device (or battery) as a charging/discharging adjustment mechanism. In contrast, Japanese Patent Laying-Open No. 2008-167620 (PTL 2) describes a power supply device in a vehicle having a main power storage device and a plurality of sub power storage devices mounted therein, that provides a converter associated with the main power storage device and a converter shared by the plurality of sub power storage devices. This configuration can achieve a reduced number of converters and also an increased storable amount of energy.
In particular, the configuration described in PTL 2 has one of the plurality of sub power storage devices selectively connected to the converter to allow the main power storage device and the selected sub power storage device to supply electric power to drive an electric motor for driving a vehicle. In the power supply device when the sub power storage device in use has a decreased state of charge (SOC) a different sub power storage device is connected to the converter to use the plurality of sub power storage devices sequentially to allow stored electric energy to be used to achieve increased electric vehicle (EV) travelable distance.